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ADS805E1K bảng dữ liệu(PDF) 9 Page - Texas Instruments |
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ADS805E1K bảng dữ liệu(HTML) 9 Page - Texas Instruments |
9 / 20 page ADS805 9 SBAS073B www.ti.com FIGURE 2. DC-Coupled, Single-Ended Input Configuration with DC-level Shift. INPUT FULL-SCALE REQUIRED MODE RANGE VREF CONNECT TO Internal 2Vp-p +1V SEL VREF Internal 5Vp-p +2.5V SEL GND Internal 2V ≤ FSR < 5V 1V < VREF < 2.5V R1 VREF and SEL FSR = 2 • VREF VREF = 1 + (R1/R2)R2 SEL and Gnd External 1V < FSR < 5V 0.5V < VREF < 2.5V SEL +VS VREF Ext. VREF TABLE I. Selected Reference Configuration Examples. V IN IN IN CM 22 Ω 22 Ω 100pF R T 100pF + 4.7µF 0.1µF ADS805 1:n 0.1µF R G FIGURE 3. Transformer-Coupled Input. REFERENCE OPERATION Integrated into the ADS805 is a bandgap reference circuit including logic that provides either a +1V or +2.5V reference output, by simply selecting the corresponding pin-strap con- figuration. Different reference voltages can be generated by the use of two external resistors, which will set a different gain for the internal reference buffer. For more design flexibil- ity, the internal reference can be shut off and an external reference voltage used. Table I provides an overview of the possible reference options and pin configurations. offset. The selection criteria for an appropriate op amp should include the input bias current, output voltage swing, distortion, and noise specification. Note that in this example the overall signal phase is inverted. To reestablish the original signal polarity, it is always possible to interchange the IN and IN connections. SINGLE-ENDED-TO-DIFFERENTIAL CONFIGURATION (TRANSFORMER-COUPLED) In order to select the best suited interface circuit for the ADS805, the performance requirements must be known. If an ac-coupled input is needed for a particular application, the next step is to determine the method of applying the signal; either single-ended or differentially. The differential input configuration may provide a noticeable advantage of achiev- ing good SFDR performance based on the fact that, in the differential mode, the signal swing can be reduced to half of the swing required for single-ended drive. Secondly, by driving the ADS805 differentially, the even-order harmonics will be reduced. Figure 3 shows the schematic for the suggested transformer-coupled interface circuit. The resistor across the secondary side (RT) should be set to get an input impedance match (e.g., RT = n2 • RG). One application example that will benefit from the differential input configuration is the digitization of IF signals. The wide track-and-hold input bandwidth makes the ADS805 well suited for IF down conversion in both narrow and wideband applications. The ADS805 maintains excellent dynamic per- formance in multiple Nyquist regions covering a variety of IF frequencies (see the Typical Characteristics). Using the ADS805 for direct IF conversion eliminates the need of an analog mixer along with subsequent functions like amplifiers and filters, thus reducing system cost and complexity. V IN 2Vp-p 0 +1V –1V R F R IN NOTE: R F = RIN, G = –1 +V S +V S OPA691 ADS805 R S 50 Ω R 3 2k Ω 22pF 10 µF + +2.5V R 2 R 1 R 4 2k Ω IN IN REFB (+1V) V REF SEL REFT 0.1 µF 0.1 µF |
Số phần tương tự - ADS805E1K |
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Mô tả tương tự - ADS805E1K |
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